Modern technologies including miniaturization, microelectronics, nonlinear optics, solar energy accumulation and conversion, and others have stimulated an increasing demand for ultrathin polymer film materials.
Plasma thin films are now generated in one of two standard ways. First, gas phase monomers are induced by plasma activation to polymerize onto a substrate at free radical sites. Alternatively, polymer-like molecules in the gas phase are exposed to a high energy plasma whereupon the molecules fragment and disassociate randomly and then form an irregular structure as individual random fragments are interlinked onto a substrate at free radical sites. During conventional cross-linking processes (curing and post-curing reactions), polymer films develop three-dimensional networks but as a result of significant topographical reorganizations, the deposited materials develop cracks that can cause drifts and interruptions in metal circuitry and can result in structural failure in other materials.
The selection of a polymer thin film for a specific application is generally dictated by a combination of properties such as electrical, thermal and mechanical characteristics and by the processing behavior of these materials.
During the fabrication of electronic or optical devices, polymer films must survive in hostile thermal (thermal cycling), chemical (exposure to solvents and curing agents), mechanical (scratching, bending) and sometime radiation (photo bleaching, ion beam technologies) environments and maintain their characteristics of modulus, thermal expansion and fluid transport in the polymer within certain limits. Inability to maintain these parameters leads to undesired phenomena like delamination, cracking, etc. Residual stress also represents a significant obstacle in ultrathin film applications.
In the field of barrier coatings, cracking and permeability of barrier layers are common problems that arise from inherent structural weaknesses in the barrier materials, when materials are deposited using the standard plasma thin film deposition methods.
In the field of microelectronic technologies, the development of high-density interconnections through multi-layer, multi-chip packages is essential to propagate high-speed signals with minimal delay and distortion. The electrical functionality, heat dissipation, and environmental reliability properties of the products depend directly on the structural characteristics of sandwiched polymeric layers. Conventional technologies in this field are based mainly on processible polyamide derivatives with good heat resistance, mechanical stability, chemical inertness and relatively low dielectric constant, rather than on inorganic materials such as alumina, glass or quartz. In the case of ultrathin polymeric films, the interlayer interface properties are more important than the bulk properties. These insulating polymeric films are located in a multilayer metal-polymer structure built on top of glass, alumina, silicon dioxide or ceramic substrates. However, since these substrates often contain contaminants such as solvents, trapped air or ions, the adhesion of films to substrates can be impaired. Consequently, novel deposition techniques need to be developed to produce uniform, clear polymeric thin films for strong bonding with the substrate.